1. Field of the Invention
The present invention relates to a liquid crystal display panel, and more particularly, to a liquid crystal display panel of a horizontal electric field type and a method of fabricating the same that is capable of simplifying the manufacturing process and reducing the cost.
2. Description of the Related Art
A liquid crystal displays (LCD) control light transmittance of liquid crystal using an electric field to thereby display a picture. The liquid crystal displays are largely classified into a vertical electric field type and a horizontal electric field type depending upon the direction of the electric field driving the liquid crystal material.
The liquid crystal display of a vertical electric field type drives a liquid crystal material in a twisted nematic (TN) mode with a vertical electric field formed between a pixel electrode and a common electrode arranged opposite to each other on the upper and lower substrates. The liquid crystal display of a vertical electric field type has an advantage of a large aperture ratio while having a drawback of a narrow viewing angle about 90°.
The liquid crystal display of a horizontal electric field type drives a liquid crystal in an in plane switch (IPS) mode with a horizontal electric field between the pixel electrode and the common electrode arranged in parallel to each other on the lower substrate. The liquid crystal display of a horizontal electric field type has an advantage of a wide viewing angle about 160°. Hereinafter, the liquid crystal display of a horizontal electric field type will be described in detail.
The liquid crystal display of a horizontal electric field type includes a thin film transistor substrate (i.e., a lower substrate) and a color filter substrate (i.e., an upper substrate) joined opposite to each other, a spacer for uniformly maintaining a cell gap between two substrates, and a liquid crystal material filled into the space provided by the spacer.
The thin film transistor substrate includes a plurality of signal lines and a plurality of thin film transistors for forming a horizontal electric field for each pixel, and an alignment film coated thereon to align the liquid crystal material. The color filter substrate includes a color filter for implementing a color, a black matrix for preventing a light leakage and an alignment film coated thereon to align the liquid crystal material.
FIG. 1 is a plan view illustrating a thin film transistor array substrate of a related art liquid crystal display panel of a horizontal electric type, and FIG. 2 is a cross-sectional view illustrating the thin film transistor array substrate taken along a line I-I′ in FIG. 1.
Referring to FIG. 1 and FIG. 2, the thin film transistor array substrate includes a gate line 2 and a data line 4 provided on a lower substrate 45 in such a manner to intersect each other, a thin film transistor 6 provided at each intersection, a pixel electrode 14 and a common electrode 18 provided at a pixel area defined by the intersection structure for the purpose of forming a horizontal field, and a common line 16 connected to the common electrode 18.
The gate line 2 supplies a gate signal to a gate electrode 8 of the thin film transistor 6. The data line 4 supplies a pixel signal via a drain electrode 12 of the thin film transistor 6 to the pixel electrode 14. The gate line 2 and the data line 4 are formed in the intersection structure to define a pixel area 5.
The common line 16 is formed in parallel to the gate line with the pixel area 5 therebetween to supply a common voltage for driving the liquid crystal material to the common electrode 18.
The thin film transistor 6 allows the pixel signal of the data line 4 to be charged and maintained in the pixel electrode 14 in response to the gate signal of the gate line 2. To this end, the thin film transistor 6 includes the gate electrode 8 connected to the gate line 2, a source electrode 10 connected to the data line 4, and the drain electrode 12 connected to the pixel electrode 14. Further, the thin film transistor 6 further includes a semiconductor pattern 49 having an active layer 48, overlapping with the gate electrode 8 with having a gate insulating film 46 therebetween to define a channel between the source electrode 10 and the drain electrode 12. In the semiconductor pattern 49, an ohmic contact layer 50, located on the active layer 48 to make an ohmic contact with the data line 4, the source electrode 10, and the drain electrode 12, is further included.
The pixel electrode 14 is connected, via a contact hole 17, to the drain electrode 12 of the thin film transistor 6 and is provided at the pixel area 5. Particularly, the pixel electrode 14 includes a first horizontal part 14a connected to the drain electrode 12 and provided in parallel with adjacent gate lines 2, a second horizontal part 14b overlapping with the common line 16, and a finger part 14c provided in parallel between the first and second horizontal parts 14a and 14b. 
The common electrode 18 is connected to the common line 16 and is formed of the same metal as the gate line 2 and the gate electrode 8 at the pixel area 5. Specifically, the common electrode 18 is in parallel with the finger part 14c of the pixel electrode 14 at the pixel area 5.
Accordingly, a horizontal electric field is formed between the pixel electrode 14 to which a pixel signal is supplied via the thin film transistor 6 and the common electrode 18 to which the common voltage is supplied via the common line 16. Specifically, the horizontal electric field is formed between the finger part 14C of the pixel electrode 14 and the common electrode 18. Liquid crystal molecules arranged in the horizontal direction between the thin film transistor array substrate and the color filter array substrate by such a horizontal electric field are rotated due to a dielectric anisotropy. Transmittance of a light transmitting the pixel area 5 is differentiated depending upon the extent of the rotation of the liquid crystal molecules, thereby implementing a gray level scale.
To form the thin film transistor array substrate of the related art liquid crystal display panel of a horizontal electric field type, a photolithography using at least four masks is used.
More particularly, a gate pattern including the gate electrode 8, the common electrode 18 and the common line 16 is formed by using a first mask process, the semiconductor pattern 49 and a source/drain pattern are formed by using a second mask process, a passivation film 52 having the contact hole 17 is formed by using a third mask process, and the pixel electrode 14 is formed by using a fourth mask process. Each mask process includes a lot of processes such as applying photo-resist, exposing, developing, cleaning, and inspection processes, etc. Accordingly, it is a complicate process for manufacturing the liquid crystal display panel and leads to a major factor of the manufacturing cost of the liquid crystal display panel.